For 11 years before FBI agents nabbed him, Toshihide Iguchi lived the well-ordered life of a Wall Street workaholic in Kinnelon, New Jersey. He rose early and headed to Daiwa Bank's Manhattan office, where he was the trusted head of U.S.-government-bond trading. He took few vacations--and then only several days at a time before rushing back to the office.

He had good reason to keep his head down, according to charges brought last week by the U.S. Attorney's office in Manhattan. During those 11 years, the office said, the baby-faced Iguchi made an astronomical 30,000 unauthorized transactions while trying to cover...